title: Cyclization under mild conditions of salicyloyl-dipeptides.
abstract: Carboxy-activated linear peptides 6(a-c) of general formula Sal-Xaa-Pro-ONp (Xaa = Phe: Gly; Aib) were synthesized and treated at room temperature with 1,8-diazabicyclo [5,4,0] undec-7-ene (DBU) in benzene solution. The tetrahedral adducts (oxa-cyclols) 7, 11 and 12, tautomeric forms of the corresponding 10-membered cyclodepsitripeptides, have been isolated in each of the three models examined. These adducts, which contain the hydroxylated carbon atom located at the junction between two 6-membered rings, do not show a tendency to isomerize into the corresponding macrocyclic lactones, regardless of the nature of the substituents on the C alpha carbon atom of the central residue. Partially cyclized dimeric products 8 and 13, identified as N-(Sal-Xaa-Pro)-dioxopiperazines (Xaa = Phe;Aib), have been also isolated from the cyclization reactions.
authors.affiliation: Department of Pharmaceutical Studies, University La Sapienza, Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Calcagni
authors.forename: G
authors.initials: G
authors.lastname: Luisi
authors.forename: G
authors.initials: G
authors.lastname: Lucente
authors.forename: F
authors.initials: F
authors.lastname: Pinnen
authors.forename: D
authors.initials: D
authors.lastname: Rossi
mesh_terms: D004151:Dipeptides / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011487:Protein Conformation; D012459:Salicylates / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D004151:Dipeptides; D012459:Salicylates